1. Field of the Invention
The present invention relates to a method of underfilling a semiconductor device such as a flip-chip mounted on the surface of a wiring substrate.
2. Description of the Prior Art
A conventional method of underfilling a semiconductor device comprises, or example, supplying a fluid of an underfill material, such as an ultraviolet (UV) curable reaction resin or a thermosetting resin, on the up-faced surface of a wiring substrate prior to setting of the semiconductor device upon the up-faced surface of the wiring substrate. The semiconductor device is placed on the fluid of the underfill material swelling on the up-faced surface of the wiring substrate. The underfill material is then subjected to a curing treatment while the semiconductor device is urged against the up-faced surface of the wiring substrate. The semiconductor device is thus fixed on the up-faced surface of the wiring substrate. According to this type of method, the space remaining between the set semiconductor device and the tip-faced surface of the wiring substrate is expected to completely he filled with the fluid of the underfill material, without any voids, even if the space gets smaller between the semiconductor device and the wiring substrate.
The supplied amount of the fluid needs to be accurately controlled for the individual semiconductor devices in the aforementioned method of underfilling. If the fluid is supplied too much for a semiconductor device, the fluid is allowed to overflow out of the space between the semiconductor device and the up-faced surface of the wiring substrate. The overflowing fluid may hinder the subsequent treatment or process for the wiring substrate or printed circuit board. To the contrary, if the fluid is not supplied enough, metallic input/output bumps may not be fully contained within the underfill material between the semiconductor device and the wiring substrate. In this case, a wiring pattern on the wiring substrate may not be fully covered with the underfill material between the semiconductor device and the wiring substrate. In any event, exposure of the input/output bumps and the wiring pattern may induce corrosion of the bumps and the wiring pattern, which is not preferable.
In addition, the individual semiconductor devices need to be separately subjected to a curing treatment in the aforementioned method of underfilling. A longer time should be spent for mounting the semiconductor devices on the corresponding wiring substrate. Moreover, the semiconductor device needs to be kept urged against the up-faced surface of the wiring substrate when the fluid of the underfill material is to be cured. A complicated mechanism should be employed in an underfilling apparatus accomplishing the above-mentioned method of underfilling.
It is accordingly an object of the present invention to provide a method of underfilling a semiconductor device capable of accurately controlling the supplied amount of an underfill material to the utmost, and an underfilling apparatus for a semiconductor device capable of realizing the same method.
It is another object of the present invention to provide a syringe, a printed circuit board and a method of preliminary treatment all designed to contribute to an accurate control of the supplied amount of the underfill material.
It is a further object of the present invention to a method of underfilling, a semiconductor device capable of employing an underfilling apparatus of a relatively simplified structure even if an underfill material is supplied to the surface of a wiring substrate prior to setting of the semiconductor device on the surface of the wiring substrate.
According to a first aspect of the present invention, there is provided a method of underfilling a semiconductor device, comprising: supplying a fluid of a reaction resin from a nozzle toward a surface of a wiring substrate prior to setting of the semiconductor device upon the surface of the wiring substrate; and reducing a fluidity of the fluid within the nozzle when a predetermined amount of the fluid has been discharged.
When the fluidity of the fluid is reduced in the nozzle, a partial fluid of the reduced fluidity can be obtained to define a partition mass or segment in the fluid within the nozzle. A reliable split can thus be achieved between the partition mass and the fluid discharged from the tip end of the nozzle. The split can be utilized to control the supplied amount of the fluid at a higher accuracy. The reaction resin may include a light curable reaction resin which is hardened by radiation of alight, a thermosetting resin which is hardened by heat, and the other types of reaction resins.
According to a second aspect of the present invention, there is provided a method of underfilling a semiconductor device, comprising: supplying a fluid of a light curable reaction resin from a nozzle toward a surface of a wiring substrate prior to setting of the semiconductor device upon the surface of the wiring substrate; and irradiating the fluid of the light curable reaction resin through a transparent window defined in the nozzle when a predetermined amount of the fluid has been discharged.
When the fluid within the nozzle is irradiated through the transparent window, a hardening reaction is induced in the irradiated segment of the fluid. The reduction in the fluidity can be achieved in the irradiated segment of the fluid. The irradiated segment forms a partition mass in the fluid within the nozzle in the aforementioned manner. A reliable split can thus be achieved between the partition mass and the fluid discharged from the tip end of the nozzle. The split can be utilized to control the supplied amount of the fluid at a higher accuracy. The ultraviolet ray curable reaction resin may include one which is hardened by independent radiation of an ultraviolet ray, one which is hardened by radiation of an ultraviolet ray in combination with heat, and the like.
For example, the aforementioned method may employ a syringe comprising: an opaque nozzle having a port at the tip end; an opaque container connected to the root end of the nozzle and containing a fluid of a light curable reaction resin; and a transparent window defined in the nozzle. The syringe is allowed to discharge the fluid of the light curable reaction resin from the port at the tip end in response to a pressure or the like applied to the container. When the window is irradiated, the fluidity of the fluid can be reduced in response to the irradiation in the aforementioned manner.
In place of the above-described syringe, a conventional syringe can be employed which comprises an opaque nozzle having a port at the tip end and an opaque container connected to the root end of the nozzle and containing a fluid of a light curable reaction resin, as conventionally known. In this case, a tube attachment may be coupled to the tip end of the nozzle. A transparent window is defined in the tube attachment. The fluid discharged from the nozzle is designed to pass through the tube attachment so as to flow out of the tip end of the tube attachment. When the fluid within the tube attachment is irradiated through the transparent window, the reduction in the fluidity can be achieved in the irradiated segment of the fluid in the aforementioned manner. The attachment is adapted to achieve reduction in the fluidity of the fluid without re-designing the structure of conventional syringes.
In addition, the aforementioned method may employ an underfilling apparatus for a semiconductor device, comprising: a table; a support head opposed to the table; a positioning mechanism connected to the support head so as to induce movement of the support head toward a discharge position; a dispenser connected to the support head so as to supply a pressure to the support head, and a light source designed to irradiate a predetermined irradiation area defined between the support head at the irradiation position and the table. The aforementioned syringe can be mounted on or attached to the support head in the underfilling apparatus. The fluid of the light curable reaction resin is allowed to flow out of the nozzle with the assistance of pressure supplied to the support head from the dispenser. The reduction in the fluidity can be achieved by positioning the transparent window right at the discharge position. The positioning mechanism is employed to position the transparent window.
It is preferable that the underfilling apparatus further comprises a mask member designed to block a ray of light headed toward the table. The mask member serves to prevent the fluid from being hardened immediately after the discharge from the tip end of the nozzle.
According to a third aspect of the present invention, there is provided a method of underfilling a semiconductor device, comprising: holding the semiconductor device against a down-faced surface of a wiring substrate so as to cover with the semiconductor device over a discharge opening defined in the wiring substrate; irradiating the down-faced surface of the wiring substrate; and supplying a fluid of a light curable reaction resin into the discharge opening through an entrance defined on an up-faced surface of the wiring substrate during irradiation.
The fluid introduced into the discharge opening is received against the semiconductor device. The fluid is allowed to spread in the space between the semiconductor device and the down-faced surface of the wiring substrate. The overflowing fluid can be subjected to the irradiation so that the overflowing fluid gets hardened at the outer periphery of the semiconductor device. The flow of the fluid can be blocked by the hardened light curable resin. The fluid can be restrained from excessive spread off the semiconductor device.
For example, the aforementioned method of underfilling may employ an underfilling apparatus comprising: a support head designed to reach a discharge position; a dispenser connected to the support head so as to supply a pressure to the support head; and a light source disposed below the support head at the discharged position so as to irradiate upward. The aforementioned syringe can be mounted on or attached to the support head. The syringe is only required to comprise an opaque nozzle having a port at the tip end and an opaque container connected to the root end of the nozzle and containing a fluid of a light curable reaction resin, as conventionally known.
Furthermore, according to a fourth aspect of the present invention, there is provided a printed circuit board comprising: conductive input/output pads arranged over an underfill receiving region defined on a surface of a wiring substrate; a first discharge opening defined in the wiring substrate at a dense area where the input/output pads are congested; and a second discharge opening defined in the wiring substrate at a sparse area where the input/output pads are scattered, said second discharge opening designed to spread over an area larger than that of the first discharge opening.
In general, when a semiconductor device is to be mounted on a wiring substrate, conductive bumps on the semiconductor device is received on the corresponding conductive input/output pads on the wiring substrate. In other words, the density of the conductive bumps depends on the density of the input/output pads. If the input/output pads, namely, the conductive bumps are congested, like the dense area, the fluid of the underfill material smoothly flows through a smaller space between the semiconductor device and the surface of the wiring substrate. The transfer of the fluid can be accelerated between the adjacent conductive bumps. On the other hand, even if the conductive bumps are scattered, like the sparse area, the second discharge opening of a larger area serves to accelerate the transfer of the fluid in the space between the semiconductor device and the wiring substrate without support of the conductive bumps. The first and second discharge openings may be continuous to form a single opening.
Furthermore, according to a fifth aspect of the present invention, there is provided a method of preliminary treatment for an underfill, comprising subjecting an underfill receiving region on a surface of a wiring substrate to irradiation of a plasma.
The ray of the plasma serves to clean up the surface of the wiring substrate so as to improve the wetness of the underfill receiving region. The improved wetness allows the fluid of the underfill material to smoothly spread over the surface of the wiring substrate. If the surface force can be set larger than the interfacial force of the fluid on the surface of the wiring substrate at the area surrounding the underfill receiving region, the fluid can reliably be prevented from spreading beyond the outer periphery of the underfill receiving region.
Furthermore, according to a sixth aspect of the present invention, there is provided a method of mounting a semiconductor device, comprising: supplying a fluid of a reaction resin on a surface of a wiring substrate; placing the semiconductor device on the fluid of the reaction resin over the surface of the wiring substrate: contacting an ultrasonic vibrator against the semiconductor device on the surface of the wiring substrate; and subjecting the fluid of the reaction resin to a curing treatment.
When the semiconductor device is to be mounted on the wiring substrate, an ultrasonic vibration is transmitted from the ultrasonic vibrator to the semiconductor device on the wiring substrate. The semiconductor device may be allowed to vibrate along the surface of the wiring substrate at a higher speed by a fine amplitude. The fine vibration of the semiconductor device along the surface of the wiring substrate serves to induce a frictional heat at the contact between conductive bumps on the semiconductor device and corresponding input/output pads on the wiring substrate. The frictional heat causes the bonding between the conductive bumps and the corresponding input/output pads. The semiconductor device is thus fixed on the wiring substrate. If the fluid of the reaction resin can be subjected to a common or single curing treatment after all the semiconductor devices have been mounted on the wiring substrate, the process can remarkably be facilitated. It leads to a shortened duration of the process. Moreover, after the fixation of the semiconductor on the wiring substrate, the fluid of the reaction resin can be cured and hardened without keeping urging the semiconductor device against the wiring substrate, so that a relatively simplified structure can be employed in an underfilling apparatus or a mounter. It should be noted that the reaction resin may include a light curable reaction resin which is hardened by irradiation, a thermosetting resin which is hardened by heat, and the other types of reaction resins.
It is preferable that a thin film is disposed between the semiconductor device and ultrasonic vibrator when the ultrasonic vibrator is contacted against the semiconductor device in the aforementioned method of mounting. When the ultrasonic vibrator contacts the semiconductor device in the above-described manner, the thin film is interposed between the ultrasonic vibrator and the semiconductor device. Accordingly, the thin film is allowed to catch the overflowing fluid of the reaction resin around the semiconductor device. The ultrasonic vibrator is reliably prevented from being adhered by the fluid of the reaction resin. The ultrasonic vibrator is allowed to keep a larger contact area against the semiconductor device. A reliable transmission of the ultrasonic vibration can be maintained between the ultrasonic vibrator and the semiconductor device in every operation.
In place of the employment of the thin film, a flange formed at the outer periphery of the semiconductor device may be employed to prevent the fluid of the reaction resin from adhering to the semiconductor device. The flange is designed to define a stepped surface opposed to the surface of the wiring substrate. The stepped surface of the flange serves to catch the fluid of the reaction resin overflowing out of the space between the semiconductor device and the wiring substrate. The fluid hardly flows around the flange toward the ultrasonic vibrator. In this manner, the ultrasonic vibrator can be prevented from being adhered by the overflowing fluid of the reaction resin to the utmost.
A method of producing the above-described semiconductor device may comprise: making a groove of a first width on a surface of a wafer when the semiconductor device is to be cut out from the wafer; and sawing the wafer by a second width smaller than the first width along a bottom of the groove so as to separate the semiconductor device from the wafer. Employment of this method serves to produce the flange at the outer periphery of the semiconductor device in a facilitated manner.